a) Field of the Invention
This invention relates to a photographic camera.
b) Description of the Prior Art
A finder in which a photographing system is arranged apart from a finder system is available in virtual and real image modes. In recent years, the real image mode finder which provides a good view of the visual field has come to be used in numerous cases.
The real image mode finder needs a means for erecting an image and the point of compaction of a camera is how this image erecting means is effectively arranged in the body of the camera in view of its space. In general, Porro prisms and pentagonal roof prisms are known as the image erecting means of compact designs.
The real image mode finder making use of the Porro prism is set forth, for instance, in Japanese Patent Preliminary Publication No. Sho 63-226616, which has such an arrangement as shown in FIG. 1. Specifically, a ray I passing through a finder objective lens 1 is incident at an entrance surface A.sub.1 of a Porro prism 2 on the Porro prism 2 and bent downward, as a ray II, by a reflecting surface B.sub.1. The ray II is laterally bent by a reflecting surface C.sub.1 into a ray III. By a reflecting surface D.sub.1, the ray III is turned upward into a ray IV, which is bent rearward, as a ray V, by a reflecting surface E.sub.1. The ray V emerges at an exit surface F.sub.1 from the Porro prism 2, traverses an eyepiece 3 arranged directly behind the Porro prism 2, arrives at a pupil, and is observed as an orthographic image.
The real image mode finder making use of the pentagonal roof prism is set forth, for example, in Japanese Patent Preliminary Publication No. Hei 1-309019, which has such an arrangement as shown in FIG. 2. Specifically, the ray I passing through the finder objective lens 1 is laterally bent by reflecting surfaces A.sub.2 and A.sub.2 ' of a Dach mirror 4 into the ray II. After forming an image of an object at a plane B.sub.2 disposed between the Dach mirror 4 and a pentagonal roof prism 5, the ray II enters the pentagonal roof prism 5 from an entrance surface C.sub.2 and is obliquely turned forward, as the ray III, by a reflecting surface D.sub.2. The ray III is bent rearward by a reflecting surface E.sub.2, coming to the ray IV. Finally, the ray IV emerges at an exit surface F.sub.2 from the pentagonal roof prism 5, traverses the eyepiece 3 arranged directly behind the pentagonal roof prism 5, arrives at the pupil, and is observed as the orthographic image.
Consideration is now given as to the case where the finders of the prior art mentioned above are arranged in the camera bodies. In the finder using the Porro prism as the image erecting means, the eyepiece 3 is placed directly behind a cartridge chamber of the camera, so that the Porro prism 2 lying directly before the eyepiece 3 is inevitably arranged, for example, as depicted in FIG. 3, directly above a cartridge chamber 6. Hence, the height of the camera involves at least the addition of the height of the Porro prism 2 to that of the cartridge chamber 6. Also, in order to reduce the height, the arrangement is proposed such that, for example, as shown in FIG. 4, the lower portion of the Porro prism 2 is embedded in the camera body between the cartridge chamber 6 and a photographic lens barrel 7. In this case, the Porro prism 2 is positioned to prevent the interference with the cartridge chamber 6, with the result that the width of the camera increases. Furthermore, in the case of either FIG. 3 or 4, the optical axis of incidence lies outside the cartridge chamber 6, that is, the relationship of h.sub.2 &lt;h.sub.1 &lt;h.sub.3 is brought about. Thus, in such a camera, there is a limit to the reduction of the height at the plane of incidence of the finder and the compaction cannot be expected.
As in the foregoing, the problem is encountered that the arrangement including such a Porro prism used in general has great restriction in view of the compact design of the camera body.
In the case where the pentagonal roof prism is used as the image erecting means, on the other hand, the height of the finder is about half that of the Porro prism type, but its width is needed 1.5 to 2 times that of the Porro prism type. Consequently, as shown in FIG. 5, when the prism 5 is arranged above the cartridge chamber 6 as in FIG. 3, the width of the camera body increases due to the finder.
Also, when the pentagonal roof prism 5 is disposed directly above the photographic lens barrel 7 as depicted in FIG. 6, the width does not increase, while the height is increased by the photographic lens barrel 7 and as such the effect of the compact design of the camera which may be secured by the use of the pentagonal roof prism 5 is made to diminish. Further, in the case of either FIG. 5 or 6, the optical axis of incidence lies outside the cartridge chamber 6, that is, the relationship of h.sub.2 &lt;h.sub.1 &lt;h.sub.3 is brought about. Thus, in such a camera, there is a limit to the reduction of the height at the plane of incidence of the finder and the compaction cannot be expected. Moreover, instead of two surfaces of the Porro prism, the Dach mirror 4 with considerably high angle accuracy must be used with the resultant great rise in cost.
Thus, the arrangement making use of the pentagonal roof prism has problems that the effect of the compact design of the camera is diminished and the cost is made very high.